A drill chuck for a hammer drill can have a chuck body connected to a drill spindle, the chuck body having a tool holder for the drill and an axial open passage through which the hammer action of the drill spindle is transmitted to the end of a drill bit, which is held in the tool holder between clamp jaws, which are advanced and retracted by means of a rotatable and axially nonshiftable support ring. A manually rotatable covering jacket engages the ring to rotate it and a restraining sleeve is nonrotatable on the chuck body but shiftable between two axial positions, the restraining casing having teeth on its end turned toward and directed to the support ring, and oriented to engage gearing on the support ring, whereby those teeth mesh with that gearing when the restraining casing is shoved toward and against the support ring so that the support ring is prevented from undesired rotation during operation and, when the restraining casing is pushed back from the support ring, the teeth are freed from engagement with the gearing of the support ring so that the clamp jaws may be advanced or retracted.
With this kind of drill chuck, for example constructed as shown in German patent document DE-GM No. 83 27 665 and the above-identified application, drilling waste, like borings, cuttings and powders, arising in the drilling process can contaminate and jam the chuck. Particularly when the drill is directed in the upwards direction to drill a hole from below, the drilling waste from the drill hole falls directly down into the open hollow space of the drill chuck and particularly enters the tool holder or between the working surfaces in the chuck body on the one hand and into the actuating jacket on the other hand and then accumulates in places from which it penetrates more deeply into the drill chuck. In time then these drilling wastes can impair the functioning of the drill chuck. Then the drill chuck must be taken apart and cleaned which as a rule requires expensive work not practical for one who is a layman. Particularly the engagement of the restraining casing with the support ring and the motion of the clamp jaws as they are advanced and retracted can be impaired by the drilling wastes.